The Nature of the Fornax 6 Globular Cluster with Magellan/M2FS Spectroscopy

The Fornax dwarf spheroidal galaxy is one of the most massive dwarf galaxy satellites of the Milky Way. Fornax is unusual in its large number of globular clusters relative to its stellar mass and to their survival over Hubble time is an open question. Recently, the 6th globular cluster was re-discovered based on DECam imaging from the Dark Energy Survey and astrometry/photometry from Gaia. Here I present follow-up Magellan/M2FS spectroscopy of the Fornax 6 cluster and the Fornax dSph.  Combined with literature data, I am able to identify 15-17 members of the Fornax 6 cluster confirming that it is both a star cluster and associated with the Fornax dSph. I measure a mean metallicity of [Fe/H]=-0.7 making it the most metal-rich of Fornax globular clusters (-1.4 < [Fe/H] < -2.5) and it is more metal-rich than the bulk of the dSph stars. Based on its metal-rich nature, the Fornax 6 cluster is likely younger than the other Fornax clusters, with an estimated age of ~2 Gyr when compared to stellar isochrones. The metallicity and luminosity of the Fornax 6 cluster is similar to the metal-rich Sagittarius globular clusters. Understanding the Fornax globular cluster system will provide insights into the dark matter distribution of Fornax and the formation and evolution of the system.